The invention relates to a fuel supply system for internal combustion engines which includes a fuel container which is kept filled with fuel up to a constant level and which communicates through a tube with the induction tube of the engine. The amount of fuel which is metered out to the air aspirated by the engine is determined by the difference in the pressure of the fuel container and of the induction tube. The pressure in the fuel container can be altered by means of solenoid valves which function under the control of the intermittent sensor voltage of an oxygen sensor located in the exhaust line. These solenoid valves are disposed in the air conduits which lead to the air space above the fuel in the fuel container and permit connecting this air space with different portions of the induction tube in which different pressures prevail.
In order to meet the technical requirements of present day engines, fuel supply systems for internal combustion engines must automatically provide an appropriate fuel-air mixture under all operational conditions of the engine to permit complete combustion and to reduce, as much as possible, any toxic components in the exhaust gas while maintaining maximum power or least fuel consumption. For this purpose, the fuel quantity which is metered out to the engine has to be adapted extremely exactly to each and every operational state of the engine. Thus, the most favorable ratio of air to fuel must be changeable in dependence on motor variables, especially exhaust gas values, and in the fuel metering system described above, this change is effected by changing the pressure in the fuel chamber.